staging: drm/omap: dmabuf/prime mmap support

Add support for mmap'ing buffers via dmabuf.  For handling mmap of
cached buffers correctly, fault handling and PTE shootdown are used
to track dirty pages and automagically handle cache flushes before
dma access to the buffer.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>